Sharks Almost Went the Way of the Dinosaurs 19 Million Years Ago

These declines in relative and absolute shark abundance counsel that one thing occurred to shark populations about 19 million years in the past, Dr. Sibert concluded.

But there was nonetheless the query of whether or not a real extinction occurred, she stated. “We wanted to know if the sharks went extinct, or if they just became less prominent.”

To take a look at the concept of an extinction, Dr. Sibert recruited Leah D. Rubin, a marine scientist then at the College of the Atlantic in Maine. Together, they developed a framework to establish distinct teams of denticles.

The researchers settled on 19 denticle traits — resembling their form and the orientation of their ridges. Dr. Sibert and Ms. Rubin sorted roughly 1,300 denticles into 88 teams. These teams don’t correspond precisely to shark species, however seeing extra teams is an indicator {that a} shark inhabitants is extra various, the researchers proposed.

Of the 88 denticle teams initially current earlier than 19 million years in the past, solely 9 persevered afterward. The discount in shark variety means that they skilled an extinction round that point, Dr. Sibert and Ms. Rubin concluded. In reality, this occasion was most likely even more cataclysmic to sharks than the dinosaur-killing asteroid impression that occurred 66 million years in the past, they stated.

“There were just a small fraction that survived into this post-extinction world,” Dr. Siebert stated.

The results of this extinction have been possible felt round the world. The constant outcomes from the two sediment cores — separated by hundreds of miles — counsel that this was actually a “global event,” two paleontologists, Catalina Pimiento of the University of Zurich and Nicholas D. Pyenson of the Smithsonian Institution, wrote in a perspective article that accompanied the study in Science.

So far, the trigger of this die-off stays unknown. There have been no vital climatic modifications in the early Miocene, and there’s no proof of an asteroid impression round that point. “We have no idea,” stated Dr. Sibert.

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